The present invention relates to an optical logic function device, and more particularly to a bistable optical device having two stable output levels for the same input level.
Bistable optical devices, have atracted sharp interest as the main constituent elements for optical logic circuits and optical memory circuits in the future, and have now become objects of intensive research and developmental efforts. In the prior art, bistable optical devices have been realized by combining light emitting elements and light receiving elements, converting the output light from the light emitting element into electric signals and returning the electric signal to the light emitting element. It is generally necessary in a bistable optical device to inject the input light for the purpose of triggering as well as extracting the output light. In other words, there are required two optical circuits for inputting and outputting light. In the previously bistable optical device, in which one light output is used for feedback, there are needed altogether three optical circuits for inputting and outputting light.
In a conventional semiconductor laser, however, only two optical circuits are available because the two output reflectors of its resonator are used for input and output. Therefore, in order to realize a bistable optical device of the above-mentioned kind, additional circuits including a light branching element are needed besides a light emitting element and a light receiving element, resulting in not only a reduced stability but also a greater overall size of the bistable optical device, thereby making it difficult to integrate many such devices.